The song is from season 3 episode 13 of MLP:FiM.
♫ Lyrics for the song:
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[Twilight Sparkle]

Morning in Ponyville shimmers
Morning in Ponyville shines
And I know for absolute certain
That everything is certainly fine

There's the Mayor en route to her office
There's the sofa clerk selling some quills

Store owner: Morning, kid!

[Twilight Sparkle]

My Ponyville is so gentle and still
Can things ever go wrong?
I don't think that they will

Morning in Ponyville shimmers
Morning in Ponyville shines
And I know for absolute certain
That everything is certainly...